138 P. OMODEO 



America and western Africa (map, Fig. 5) and by the genera Ilyogenia (Fig. 

 10). Ocnerodrilus, and Gordiodrilus, which Hve throughout tropical Africa 

 also. Lastly there are six to eight species of Octochaetinae. Some of these 

 have been attributed to the Indo-Malagasy genus Howascolex and one to 

 the Indian genus Ramiella. It seems to me that they should be placed to- 

 gether in a genus of their own; at any rate their relationship with the Malagasy 

 and Indian forms is certain. 



To conclude, in central America and the Antilles we find fauna similar to 

 that of Africa with Indo-Malagasy elements as well as elements related to 

 that of the Chilean -Patagonian subregion wedged in between a commonplace 

 Holarctic fauna and a Neotropical fauna with a high degree of endemism. 



I should like to emphasize the relationship with the African fauna which 

 concerns five genera out of eight. We find that these five genera are abundant 

 precisely on the western coast of Africa from Guinea to Angola. Apart from 

 the representatives of the family Eudrilidae, confined to the equatorial strip of 

 the Paleotropical region, there were represented in some West African 

 collections that I have had an opportunity to study, eleven genera of which 

 five were common to Africa and central America and two to the northeastern 

 coasts of South America and Africa. 



To show the particular situation of the central American Oligochaetes 

 more clearly, I shall momentarily modify the method of exposition that I have 

 been following and instead of listing the faunas of each region and their 

 relationship, I shall here describe the distribution of the family Acantho- 

 drilidae (cf. Table 1). This family, as mentioned above, is divided into the 

 subfamily Acanthodrilinae (the most primitive), Ocnerodrilinae (generally 

 specialized for limicolous life), Octochaetinae, and Benhaminae. The 

 Acanthodrilinae are distributed in the southern countries, from Chile to New 

 Caledonia, and have in addition several genera in central and northern 

 America: the Diplocardiacea section is endemic to this latter area. The 

 Ocnerodrilinae occupy all of central America, the Brazilian subregion, 

 Africa, Madagascar, and the Oriental region. Contrarily, the Octochaetinae 

 are peculiar to New Zealand, the Oriental region, Madagascar, and are 

 missing on the African continent but reappear in central America. The 

 Benhaminae have the same distribution as the Ocnerodrilinae but they are 

 very scarce in South America (map, Fig. 7). 



Only in central America are found all four subfamilies of Acantho- 

 drilidae: following an old rule of biogeography, one should conclude that 

 this district was the center of origin and diffusion of the entire group. This is 

 possible but there remain some doubts because of the great gap between the 

 central American and austral Acanthodrilinae and between the central 

 American and Indo-Malagasian Octochetinae. However, it must be kept in 

 mind that out of all the families of earthworms the one of which we are 

 speaking here has the widest distribution and includes forms with the most 



